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Alioramus
Alioramus is moderately sized genus of the Tyrannosaurid family. It had a length of 6-7 metres, and lived in Asia in the Late Cretaceous period (75-65 million years ago). It's name means different branch. It has a long thin face and little horns on its snout. Description Alioramus remotus was estimated at 5 to 6 metres (16 to 20 ft) in length when originally described by Sergei Kurzanov in 1976.1 Kurzanov, however, did not correct for lengthening of the skull by deformation during fossilization, which may indicate a shorter overall body length for this individual. If this specimen is a juvenile, then adult Alioramus would have reached greater lengths, but no confirmed adult specimens are known.2 The skull of A. remotus was approximately 45 centimetres (18 in) long.3 In general, it is long and low, a shape typical of more basal tyrannosauroids and juveniles of larger tyrannosaurids. The premaxillary bones at the tip of the snout in Alioramus remotus have not been found, but are taller than wide in all tyrannosauroids for which they are known.2 The nasal bones are fused and ornamented with a row of five irregular bony crests that protrude upwards from the midline, where the nasal bones are sutured together. These crests all measure more than 1 centimetre (0.39 in) tall. At the back of the skull there is a protrusion, called the nuchal crest, arising from the fused parietal bones, a feature shared with all tyrannosaurids. In Alioramus, the nuchal crest is greatly thickened, similarly to Tarbosaurus and Tyrannosaurus. Like the rest of the skull, the lower jaw of Alioramus was long and slender, another possible juvenile characteristic.2 As in Tarbosaurus, a ridge on the outer surface of the angular bone of the lower jaw articulated with the rear of the dentary bone, locking the two bones together and removing much of the flexibility seen in other tyrannosaurids.4 Other tyrannosaurids had four premaxillary teeth, D-shaped in cross section, on each side. Including 16 or 17 in each maxilla, and 18 in each dentary, Alioramus had 76 or 78 teeth, more than any other tyrannosaurid.5 The braincase of A. altai was intermediate between the basal theropod and avialan conditions.6 The rest of the skeleton of Alioramus remotus is completely unknown except for three metatarsals (bones of the upper foot), but the discovery of A. altai, which is known from substantially more complete remains, has shed light on the anatomy of the genus. Classifications and systematics Paleontologists have long classified Alioramus within the superfamily Tyrannosauroidea, but because its remains were for many years poorly known, a more precise classification had remained elusive until the discovery of A. altai.2 A cladistic analysis published in 2003 found Alioramus could be further classified into the family Tyrannosauridae and the subfamily Tyrannosaurinae, alongside Tyrannosaurus, Tarbosaurus and Daspletosaurus.8 A 2004 study supported this result but suggested it was equally probable that Alioramus belonged outside the family Tyrannosauridae entirely, with its supposed juvenile characters actually reflecting a more basal position within Tyrannosauroidea.2 Another study omitted Alioramus altogether due to the only specimen's fragmentary nature.9 The discovery of A. altai in 2009 confirmed the placement of the genus within the Tyrannosaurinae. Tarbosaurus and Alioramus shared several skull features, including a locking mechanism in the lower jaw between the dentary and angular bones, and both lacked the prong of the nasal bones which connected to the lacrimal bones in all other tyrannosaurids except adult Daspletosaurus. The two genera may be closely related, representing an Asian branch of the Tyrannosauridae.48 Some specimens of Tarbosaurus have a row of bumps on the nasal bones like those of Alioramus, although much lower. The long and low shape of the only known Alioramus remotus skull indicated that it was immature when it died and might even have been a juvenile Tarbosaurus, which lived in the same time and place. The more prominent nasal crests and much higher tooth count of Alioramus, however, suggested it was a separate taxon, even if it is known only from juvenile remains,5 confirmed by the discovery of A. altai.7 Specimens identified as immature Tarbosaurus have the same tooth count as adults.1011 Recently a cladogram has been published finding Alioramus just outside Tyrannosauridae. Below is the cladogram by Loewen (2013). |2= |2=Tyrannosauridae }} }} }} }} }} }} }} }} }} Discovery and naming Category:Dinosaurs of Asia Category:Tyrannosaurs Category:Cretaceous dinosaurs